I got hold of a copy of “The Knight & The Blast Furnace” by Alan Williams. This is a ridiculously big (950 A4 pages), ridiculously expensive book (£300+, if you can find a copy – it only seems to have had a print run of about 3,000 copies) about the metalluturgy of medieval armour. It's pretty much the definitive on that subject, and quite hard to get, so I thought it might be useful to summarise what I understood as the key points here:- The constraints on developing plate armour proves to be bloom size, which is in turn constrained by furnace size; you don't get furnaces big enough until mid c14th.- The key difference in armour strength / hardness isn't the difference between iron (100-150 VPH) and unhardened steel (150-200 VPH), it's the difference between unhardened steel and hardened steel (400-800 VPH, depending on carbon content). - Strength (and thus protective value) follows from the product of hardness and thickness; the equation means that doubling thickness more than doubles strength - You harden steel by quenching it in water, then temper it by reheating to remove the stresses that would otherwise make it brittle.- Medieval steel isn't modern steel, and you don't have good temperature control. This means you have only about 5 seconds to quench it (v 15 with modern steel) and if you let the temperature go too high while tempering, you remove the hardness as well as the brittleness- The result is that some medieval armour is slack / interupt quenched, giving semi hardened steel (VPH 3-400) but avoiding the risk of over tempering- C15th italian armour is almost always steel, and most of the examples bearing armourer's marks (ie quality stuff) is either hardened or semi hardened. Only about 25% of the cheaper unmarked stuff is even semi-hardened; it's clearly worth getting that suit of milanese plate- South Germany only starts producing hardened steel armours towards the end of the c15th; before 1450 they might (50/50 be steel rather than iron, but are almost never hardened. By the late 15th, the south Germans have caught up with the italians, (most of the good armour is steel, and almost all of it is fully hardened, with the rest semi hardened) and it's at that point they start marking armour with armourers marks. - Armour from outside those areas (north germany, netherlands, france, england) is hard to identify, but seems to be bottom-end stuff; there's a good reason it is cheap (...and south germans complain at it undercutting them) and why englishmen who can afford it send to milan rather than buy locally. Think of it all as munition quality stuff, except for the English Greenwich armours, which are after our period and made by imported craftsmen- Fire gilding (really, really fashionable after about 1510) means painting the armour with gold in a mercury amalgam, then heating to drive off the mercury. Unfortunately, the temperature required is enough to remove the hardening from your armour, and after that point even the best italian armourers stop even trying to harden armour. It's genuinely more important to be pretty than safe- The germans find a way to combine the gilding and tempering processes, and can fire gild hardened armour. This essentially requires that a few families of gilders and armourers marry each other's daughters, cousins etc for three generations, and don't tell anyone else how to- Post 1550 pretty much all the armour you get is straight iron, and your improve the resistance by making it thicker rather than hardening it. The protection is the same, but it's significantly heavier

Talking about the effectiveness of “plate armour” is thus like talking about the effectiveness of “guns”; we need to define what we're talking about much more closely

Williams has done an equivalent book about swords "The Sword and the Crucible" which is still in print, at the achievable if expensive price of £130. TBH I found that less of a game changer than the armour book above

Thanks for this Neil. I know Alan and have read sections of his book over the years, but I've never actually owned a copy. This is a good summary and does telly with everything I can remember from the various lectures he has done at the Wallace Collection and elsewhere.